The present invention relates to color measurement instruments, and more particularly to strip reading color measurement instruments and spot reading color measurement instruments.
A wide variety of color measurement instruments are known for many and varied applications. These instruments are used, for example, to accurately determine the color of materials such as printed matter, photographic matter, paints, textiles, and plastics. More specifically, the instruments measure the spectral distribution within the visible color spectrum of light reflected by, or transmitted through, a sample. The color measurement engines within color measurement instruments can be spectrophotometers, colorimeters, densitometers, or other devices used to measure color.
One type of color measurement instrument is a strip reading instrument. Such an instrument typically sits on a horizontal surface (e.g. a countertop) and draws a strip to be measured through the instrument and past a color measurement engine. The engine periodically measures the color of the moving strip. An exemplary strip reading instrument is disclosed in U.S. Pat. No. 6,198,536 issued Mar. 6, 2001 to Baker.
A second type of color measurement instrument is a spot reading instrument. Such an instrument is typically a handheld unit that can be aligned with a particular color or spot to be measured. When manually aligned, the instrument is actuated to read the color or spot.
Both strip reading instruments and spot reading instruments are dedicated to a single function (e.g. strip reading or spot reading). Consequently, a user desiring to read both strips and spots must purchase two separate instruments.
Spot reading instruments typically include a spring-loaded shoe that carries a targeting system to assist the user in accurately positioning the instrument with respect to the spot to be measured. After being accurately positioned, the instrument is closed against the shoe, overcoming the spring force. The measurement is taken when the instrument is closed against the shoe. The shoe provides precise vertical positioning of the optics in the instrument with respect to the read plane of the sample being measured. The instrument is then released whereupon the spring-loaded shoe reopens the instrument. The shoe and targeting system typically are intended to remain connected to the instrument. However, on certain occasions, removal of the shoe and target may be desired. When the shoe is removed, it is subject to damage, soiling, and possible loss.
All color measurement instruments must be calibrated from time to time. Such calibration usually is performed using one or more reference colors, whose properties are known. During calibration, the instrument reads the reference color(s) and then configures itself based on the differences between the known properties and the measured properties. Typically, the references colors are used relatively infrequently, which results in several problems. First, the reference colors can be misplaced. Second, the reference colors can be damaged, for example, by scratching. Third, the references colors can become soiled. Both damage and soiling can damage the reference color(s), thereby decreasing the accuracy and thereby the utility of the calibration function.